• journal_title：The Canadian Mineralogist
• Contributor：Petr Černý ; T. Scott Ercit ; Sten-Anders Smeds ; Lee A. Groat ; Ron Chapman
• Publisher：Mineralogical Association of Canada
• Date：2007-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.45.2.185
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：45
• issue：2
• firstpage：185
• section：Articles

Niobium–tantalum-oxide minerals from five localities with moderately to highly fractionated granitic pegmatites were examined for their Zr and Hf contents. Wodginite was found to contain up to 9.59 ZrO₂ and 1.15 wt.% HfO₂, and columbite-group minerals, up to 1.26 and 0.12 wt.%, respectively. The Zr/Hf value is decidedly high in columbite-group minerals (13 to 6) relative to wodginite (4 to 1). Coexisting wodginite-group and columbite-group minerals behave similarly with respect to the overall behavior of Zr + Hf and with respect to the partitioning of Zr versus Hf. In individual pegmatite bodies, no systematic changes in Zr + Hf or Zr/Hf are discernible among the various zones. However, a positive correlation of Zr + Hf with Sn, Mn and Ta is locally observed, and a negative correlation with Ti. No clear trends are shown by Zr/Hf. The Zr/Hf value in the (Nb,Ta)-oxide minerals generally corresponds to its range in associated zircon–hafnon. Considerable depolymerization of highly fractionated, (F, B, P)- and H₂O-rich pegmatite-forming melts, in part alkaline in boundary layers (particularly significant in final stages of consolidation), is responsible for shifting oxygen coordination of Zr and Hf from [8]- to [6]-fold. Consequently, the abundance of zircon decreases, and the (Nb,Ta)-oxide minerals become geochemically significant carriers of Zr and Hf. This effect apparently operates not only in granitic pegmatites but also in other granite-related environments.